Doppler Tracking

[The Sky Dart]

We successfully tracked a model rocket using doppler frequency measurements. Detailed description can be found here: https://sites.google.com/site/theskydar ... r-tracking. It's a bit skinny, but all main elements and results are reflected.

A 2 kHz buzzer was attached to a small model rocket. Its sound was recorded before and during a flight. After that the record was analysed using a audio frequency analyser. A doppler frequency shift was measured and corresponding speed was calculated.

[U.S. Water Rockets1]

We successfully tracked a model rocket using doppler frequency measurements. Detailed description can be found here: https://sites.google.com/site/theskydar ... r-tracking. It's a bit skinny, but all main elements and results are reflected.

A 2 kHz buzzer was attached to a small model rocket. Its sound was recorded before and during a flight. After that the record was analysed using a audio frequency analyser. A doppler frequency shift was measured and corresponding speed was calculated.

Guys, this is absolutely brilliant. Very nice idea. You guys should be really proud of this concept. Thanks for posting your findings.

[The Sky Dart]

We successfully tracked a model rocket using doppler frequency measurements. Detailed description can be found here: https://sites.google.com/site/theskydar ... r-tracking. It's a bit skinny, but all main elements and results are reflected.

A 2 kHz buzzer was attached to a small model rocket. Its sound was recorded before and during a flight. After that the record was analysed using a audio frequency analyser. A doppler frequency shift was measured and corresponding speed was calculated.

Guys, this is absolutely brilliant. Very nice idea. You guys should be really proud of this concept. Thanks for posting your findings.

Unfortunately we don't have any water rocket ready for a flight at the moment. It would be really nice if someone could attach a buzzer to one and record it for us. Ideally it'll be interesting to compare the doppler data to an altimeter record.

[U.S. Water Rockets1]

We successfully tracked a model rocket using doppler frequency measurements. Detailed description can be found here: https://sites.google.com/site/theskydar ... r-tracking. It's a bit skinny, but all main elements and results are reflected.

A 2 kHz buzzer was attached to a small model rocket. Its sound was recorded before and during a flight. After that the record was analysed using a audio frequency analyser. A doppler frequency shift was measured and corresponding speed was calculated.

Guys, this is absolutely brilliant. Very nice idea. You guys should be really proud of this concept. Thanks for posting your findings.

Unfortunately we don't have any water rocket ready for a flight at the moment. It would be really nice if someone could attach a buzzer to one and record it for us. Ideally it'll be interesting to compare the doppler data to an altimeter record.

Our rocket would need a loudspeaker to record, as far up as it goes.

Unless you can recommend a sensitive parabolic microphone we could use to listen to the rocket with only a small speaker onboard from far away.

[The Sky Dart]

Our rocket would need a loudspeaker to record, as far up as it goes.

Unless you can recommend a sensitive parabolic microphone we could use to listen to the rocket with only a small speaker onboard from far away.

It doesn't really matter. Any mono-frequency buzzer will do. Something like this http://www.maplin.co.uk/Module.aspx?Mod ... &U=strat15. (You'll probably have to find an US equivalent). The most important thing is to make sure that it produces a clear harmonic without any significant spurious emission. Check it with a spectrum analyser, or give me a sample record file and I'll check it for you. To record the sound we used my smart phone, which could pick up the buzzer from about 100...150 meter. Video recorder in our photo camera has even better sensitivity.

The point is to see the acceleration phase and the beginning of the deceleration phase. From that time to the apogee can be approximated without any problems from the speed curve, that will be something like this: http://sites.google.com/site/theskydart ... &width=317
Ideally it would be very good to compare these measurements to tracking altimeter if you have one of course.

[U.S. Water Rockets1]

Our rocket would need a loudspeaker to record, as far up as it goes.

Unless you can recommend a sensitive parabolic microphone we could use to listen to the rocket with only a small speaker onboard from far away.

It doesn't really matter. Any mono-frequency buzzer will do. Something like this http://www.maplin.co.uk/Module.aspx?Mod ... &U=strat15. (You'll probably have to find an US equivalent). The most important thing is to make sure that it produces a clear harmonic without any significant spurious emission. Check it with a spectrum analyser, or give me a sample record file and I'll check it for you. To record the sound we used my smart phone, which could pick up the buzzer from about 100...150 meter. Video recorder in our photo camera has even better sensitivity.

The point is to see the acceleration phase and the beginning of the deceleration phase. From that time to the apogee can be approximated without any problems from the speed curve, that will be something like this: http://sites.google.com/site/theskydart ... &width=317
Ideally it would be very good to compare these measurements to tracking altimeter if you have one of course.

Where do you mount the buzzer so that you can hear it with the microphone? We might be able to mount the speaker just above our nozzle and tape the wires along the side of the rocket to the electronics payload bay up top.

[The Sky Dart]

Where do you mount the buzzer so that you can hear it with the microphone? We might be able to mount the speaker just above our nozzle and tape the wires along the side of the rocket to the electronics payload bay up top.

Ideally the buzzer opening should face downwards, but for the obvious reason such design could be impractical. For our test purposes we just typed it to the outer skin of a test rocket. Of course there is no ideal solution.

In fact it makes results even more interesting,. If the rocket rolls, you may be able to detect it in the doppler measurements as a periodical variation of the frequency. For example on this picture (http://7425399502463090470-a-1802744773 ... edirects=0) some irregularity of the received frequency after the ejection was caused by rolling of the rocket.

You interest is much appreciated. Thank you very much.

[U.S. Water Rockets1]

For the most accurate calculations of the doppler effect, do you not need to take into account the ambient atmospheric pressure? Doesn't the speed of sound also change with altitude due to the air pressure gradient? It further complicates the math you need to do in order to come up with the most accurate results.

[The Sky Dart]

The most important factor is the air temperature. Air is almost an ideal gas, thus the speed of sound should not dement upon its pressure or density very much. The speed of sound changes with altitude, but mostly due to a change in the temperature. However, I don’t consider the factor to be very important at this stage due. For example for +20 degree the speed is about 343 m/s. For +15 it’s around 340 m/s. The change is small comparing to other inaccuracies. I ignore this factor for now.
Another factor to consider is wind speed. However, it a bit more difficult to take into account and for now I ignore this factor as well.

I agree, getting the most accurate result requires considering many factor. However, the main original purpose of the experiment was educational. I set it up to illustrate some physical principals to my son. As any such experiment it’s very far from proper scientific set up. At least at the moment. It’s just fun.

The next step I’m planning is to perform 3D triangulation which theoretically can provide all three coordinates x, y and z. I was going to do the first pass at the last launch meeting a couple of weeks ago, but it was cancelled due to strong wind. In absence of data, I did a simplified 2D experiment. A buzzer was attached to a 1 meter string and swivelled around. The sound was recorded with a couple of mics with a base of about 40 meters. I can’t say it pin-points the buzzer location, but the accuracy is sufficient to establish direction of the rotation and approximate coordinate. I’ll post the results later.

[The Sky Dart]

A short video with results of our latest doppler experiment.

[youtube][/youtube]